Tests of soil fertility following repeated applications of MCPA, tri-allate, simazine and linuron

The following herbicides were applied annually from 1963 to experimental plots of appropriate crops grown in monoculture: MCPA 1.7 kg ha^?1, triallate 1.7 kg ha^?1, simazine 1.7 kg ha^?1 and linuron 0.84 kg ha^?1 (applied twice per year). Before the eighth treatment in 1970, nutrient status, pH and growth in greenhouse tests of a range of plants were similar in soils from treated and control plots. There were no significant differences in yield when several test crops were grown in the field plots in 1977. In a similar experiment which ran for 6 years, the same herbicides were applied twice per year at twice the above rates on each occasion (three times a year at 1.7 kg ha^?1 in the case of linuron) to uncropped plots. Three years after the last treatment, there were no differences in extractable nutrients, pH, soil structure and crop yield on treated or control plots. These results support the conclusion from the main monitoring of the experiments reported elsewhere that annual treatments with these herbicides have had no adverse affect on the soil.     

Residues of atrazine, simazine, linuron and diuron after repeated annual applications in a peach orchard

Annual applications of the herbicides atrazine, simazine, linuron and diuron at 45 kg/ha were made to the same plots for 9 consecutive years from 1963 to 1971 in a peach (Prunus persica (L.) Batsch.) orchard located on sandy loam soil near Harrow, Ontario. Soil samples from these plots were collected in late October for the last 3 years (1969–1971) and trees were cut down in December, 1969. Herbicide residues were determined by bioassays based on the fresh and dry weight of oats (Avena sativa L.) and in one year results were confirmed by chemical analysis. Significant accumulation of herbicides was not observed. The maximum residue levels measured in October over the 3 years of sampling were 7′3 kg/ha for diuron, 3–8 kg/ha for linuron, 1–6 kg/ha for simazine and 04 kg/ha for atrazine in the top 15 cm of the soil profile. Simazine and atrazine showed a rapid decrease in amount after treatment but diuron and linuron were degraded more slowly. Measurable residues of all herbicides were confined to the upper 15 cm of the soil profile and the majority of herbicide remained in the 0–5-cm soil layer. Oats were planted in the orchard plots from 1972 to 1974 to follow the disappearance of the herbicides. All herbicides caused highly significant yield decreases in 1972, atrazine causing the least (38%) and diuron the greatest (86%) reductions. Diuron reduced the yield of oats in 1973 and caused a highly significant decrease in the weight of young oat plants in 1974.     

Simulation of herbicide persistence in soil .II. Simazine and linuron in long-term experiments

The rates of degradation of simazine and linuron were measured in soil from plots not treated previously with these herbicides. Degradation of both compounds followed first-order kinetics and soil temperature and soil moisture content had a marked effect on the rate of loss. With linuron, half-lives increased from 36 to 106 days with a reduction in temperature from 30° to 5°C at 4% soil moisture, and from 29 to 83 days at 12% soil moisture. Similar temperature changes increased the half-life of simazine from 29 to 209 days and from 16 to 125 days at soil moisture contents of 4 and 12% respectively. A computer program which has been developed for simulation of herbicide persistence was used in conjunction with the laboratory data and the relevant meteorological records for the years 1964 to 1968 in order to test the model against previously published field persistence data for the two herbicides. The results with simazine showed a close correspondence between observed and predicted residue levels but those for linuron, particularly in uncropped plots, were satisfactory for limited periods only.     

Control of Avena fatua and Fagopyrum tataricum with tank mixtures of linuron or linuron + MCPA and sequential applications of linuron, and post-emergence A. fatua herbicides

Linuron (0.21 and 0.28 kg/ha) and linuron + MCPA (0.21+0.56 kg/ha) in a tank mixture with field rates of barban, difenzoquat and flamprop-methyl reduced the phytotoxicity of these herbicides to Avena fatua. When linuron was applied immediately following or 6 days after the A. fatua herbicides no reduction in phytotoxicity to A. fatua occurred, suggesting that the antagonism may be occurring as a result of physical or chemical incompatability when the herbicides are mixed together. The possibility of obtaining broad-spectrum weed control with one trip over the field by applying linuron and one of these wild oat herbicides separately but at the same time using a double-boom, double-tank system deserves evaluation. When linuron was applied in a tank mixture (0.21 and 0.28 kg/ha), immediately after, or 6 days after diclofop-methyl (0.70 kg/ha), there was no reduction of A. fatua control, and wheat tolerance to the tank mixture was good. This tank mixture offers potential for control under field conditions of A. fatua and some broad-leaved weeds in one spray operation. Linuron + MCPA (0.21+0.56 kg/ha) in a tank mixture severely reduced A. fatua control with diclofop-methyl. No loss of phytotoxicity to Fagopyrum tataricum occurred when the A. fatua herbicides tested were tank mixed with linuron or linuron + MCPA. Lutte contre Avena fatua et Fagopyrum tataricum avec des mélanges extemporanés de linuron ou de linuron + MCPA et des applications successives de linuron et d'herbicides de postlevée actifs contre A. fatua     

The effects of repeated applications of the molluscicide metaldehyde and the biocontrol nematode Phasmarhabditis hermaphrodita on molluscs, earthworms, nematodes, acarids and collembolans: a two-year study in north-west Spain

Over two years, six consecutive field experiments were done in which the chemical molluscicide metaldehyde and the nematode biocontrol agent Phasmarhabditis hermaphrodita (Schneider) were applied at the standard field rates to replicated mini-plots successively planted with lettuce, Brussels sprouts, leaf beet and cabbage, to compare the effectiveness of different treatments in reducing slug damage to the crops. Soil samples from each plot were taken prior to the start of the experiments, and then monthly, to assess the populations of slugs, snails, earthworms, nematodes, acarids and collembolans. The experiments were done on the same site and each plot received the same treatment in the six experiments. The six treatments were: (1) untreated controls, (2) metaldehyde pellets, (3 and 4) nematodes applied to the planted area 3 days prior to planting without or with previous application of cow manure slurry, (5) nematodes applied to the area surrounding the planted area 3 days prior to planting, and (6) nematodes applied to the planted area once (only in the first of the six consecutive experiments). Only the metaldehyde treatment and the nematodes applied to the planted area at the beginning of each experiment without previous application of manure significantly reduced slug damage to the plants, and only metaldehyde reduced the number of slugs contaminating the harvested plants. The numbers of slugs, snails and earthworms in soil samples were compared among the six treatments tested: with respect to the untreated controls, the numbers of Deroceras reticulatum (Müller) were significantly affected only in the metaldehyde plots, and the numbers of Arion ater L only in the plots treated with nematodes applied to the planted area 3 days prior to planting without previous application of manure; numbers of snails (Ponentina ponentina (Morelet) and Oxychilus helveticus (Blum)) were not affected by the treatment. The total numbers of all earthworm species and of Lumbricus spp were unaffected by the treatment, but Dendrobaena spp increased significantly in the plots treated with manure. The numbers of nematodes, acarids and collembolans in soil samples were compared between the untreated controls and the treatments with nematodes applied 3 days prior to planting to the planted area or to the surrounding area, without previous application of manure: the treatment had a significant effect on the number of nematodes in soil samples, but acarids and collembolans were unaffected.     

Genetic variation in herbicide resistance in scentless mayweed (Tripleurospermum inodorum (L.) Schultz Bip.) II. Intraspeciffc variation in response to ioxynil and MCPA, and the role of spray retention characteristics

Forty-eight populations of Tripleurospermum inodorum (L.), Schultz Bip. (scentless mayweed) were collected from southern Britain and northern France between 1970 and 1972 and screened simultaneously for resistance to the herbicides ioxynil and MCPA. The mean fresh weights per plant in different population samples sprayed with ioxynil at 28 mg/m² a.i. ranged from 2·2 to 39·5% of those of the corresponding controls, with a mean for all populations of 20·0 ± 1·09%, and the mean fresh weights per plant in different population samples sprayed with MCPA at 175 mg/m² a.e. ranged from 10·3 to 60·1% of those of the corresponding controls, with a mean for all populations of 43·0 ± 1·60%. Resistance to ioxynil differed significantly between populations from different geographic areas but showed no correlation with spraying history. Resistance to MCPA also differed significantly between populations from different geographic areas, and showed a strong positive correlation with ioxynil resistance, but MCPA resistance was significantly greater in populations with a history of heavy spraying than in other populations. Spray retention and other physical characteristics were measured in six populations, but showed no correlation with herbicide resistance. It is suggested that most of the differences in herbicide resistance between populations of T. inodorum are side effects of genotypic differentiation in physiological characters not directly related to herbicide resistance, but that there has been some direct selection for resistance to MCPA.     

Pesticide residues in the total diet in England and Wales, 1966–1967: IV.—Mercury content of the total diet

Results are given of determinations of the mercury content of each of the 7 composite food groups into which samples of the total diet were divided. In the very few sub-samples in which mercury was detected, the levels found were very low and close to the limit of detection by the colorimetric method used.     

The origins of selectivity and performance of a new pre-emergence bleaching herbicide,WL 110547. Part II: Plant and environmental factors influencing biological activity

Pre-emergence applications of the novel tetrazole herbicide WL 110547 control a number of economically important grass and broad-leaved weed species in small grain cereals. To assess the influence of plant and environmental factors on the biological performance of WL 110547, a series of tests were carried out under controlled conditions and, where appropriate, comparisons were made with field observations. When presented with the maximum opportunity for compound uptake in the absence of soil, differences in the degree of susceptibility to WL 110547 were observed amongst both monocotyledonous and dicotyledonous species, although the latter group generally showed higher levels of phytotoxicity. This species susceptibility to WL 110547 was unaffected by temperature. Increasing the sowing depth in soil decreased the level of effect of WL 110547 on a number of monocotyledonous species, although small-seeded species (e.g. blackgrass, annual meadow grass), emerging from deep in the soil profile, subsequently developed levels of phytotoxicity comparable to, or even greater than, shallow-planted seedlings. This was attributed to less vigorous seedlings, emerging from depth, that were unable to regenerate new tissue and grow away from a treated soil layer. Reduced growth rates of wild oat, blackgrass and speedwell, induced by low temperatures, also increased the phytotoxicity of WL 110547. Furthermore, applications of WL 110547 during seedling emergence maximised herbicide effect, as did seedling emergence through moist rather than dry soil. The results are discussed in relation to the mobility of the herbicide in soil, the mode of action of WL 110547, its availability to the plant and the duration of contact between emerging shoot and treated soil layer.     

Pesticide residues in foodstuffs in England and Wales. Part II: Inorganic bromide ion in cucumber,tomato and self-blanching celery grown in soil fumigated with bromomethane,and the ‘natural’ bromide ion content in a range of fresh fruit and vegetables

Surveys of inorganic bromide ion residues in tomatoes, cucumbers and selfblanching celery, commercially produced in England following soil sterilisation with bromomethane, have been carried out since 1979. The mean bromide ion level in 29 late-season cucumber samples was approximately 28 mg kg⁻¹ and ranged up to 109 mg kg⁻¹. Analysis of 242 tomato samples gave estimated mean bromide ion levels per plant ranging from 6 to 187 mg kg⁻¹ in fruit picked throughout the season from seven holdings, on six of which bromomethane had been used fairly recently prior to planting. A statistically significant fall in bromide levels over the growing season was shown on four of the sites. In 38 samples of self-blanching celery, the mean bromide ion level was 104 mg kg⁻¹ even though the mean interval between fumigation and planting was in excess of 1 year. Retail surveillance indicated that a large number of crops are likely to have bromide ion levels below 10mg kg⁻¹.     

Regeneration capacity of the small clonal fragments of the invasive Mikania micrantha H.B.K.: effects of the stolon thickness,internode length and presence of leaves

Mikania micrantha H.B.K., one of the top 10 worst weeds in the world, is now spreading quickly in southern China. Disturbance can fragment and spread the stolons of M. micrantha. A greenhouse experiment was conducted in order to assess the regeneration capacity of single‐node fragments with varying stolon thickness (diameters of 3.01, 2.49 and 1.96 mm), internode lengths (2 and 8 cm) and leaf presence status (with and without leaves). The results indicated that an increasing stolon thickness, internode length and the presence of leaves all increased the survival rate of the clonal fragments. An increasing stolon thickness, internode length and the presence of leaves also increased the growth of the clonal fragments and the presence of leaves exhibited the strongest effect. An increasing internode length and the presence of leaves also reduced the amount of time that was needed for emergence, while the effect of the stolon thickness was not significant. None of the effects of the interactions was significant, although the interaction between the stolon thickness and the internode length was nearly significant for fragment survival. These results suggest that M. micrantha has developed a strategy to cope with disturbance by storing reserves in the stolons and leaves, which could increase its regeneration capacity after fragmentation. Currently, the management of M. micrantha (such as manual or mechanical control) should avoid the generation of the small clonal fragments of M. micrantha, while repeated control with short time intervals is necessary in order to prevent reinvasion from the stolon fragments.     

The kinetics of insecticide action. Part II: The relationship between the pharmacokinetics of substituted benzyl (1RS)-cis,trans-chrysanthemates and their relative toxicities to mustard beetles (Phaedon cochleariae fab.)

A mathematical model describing insect pharmacokinetics has been applied to data describing the penetration and elimination of a series of pyrethroid analogues [the methylbenzyl (1 RS)-cis, trans-chrysanthemates], applied to mustard beetles. The three parameters of the model (k_p, k_e and λ) have been estimated for each compound. The influence of chemical structure on pharmacokinetics, investigated using canonical correlation analysis, is discussed in relation to relative toxicity and knockdown action. In general, physicochemical properties which result in a slow flow of insecticide through the insect are associated with high toxicity. A large proportion (84%) of the variation in relative toxicity has been explained by resistance to elimination (1/k_e), implying that exposure of the site of action to insecticide is related to the total integral IM₂ for material (M₂) inside the insect. The remaining variation has been attributed to differences in behaviour at receptor sites. An optimum partition value (Δπ₀ ≈ 1.6) seems necessary for maximum pharmacodynamic activity in this series of compounds.